Temporal changes in VAM fungi in the cocoa agroforestry systems of central Cameroon

Abstract

In Cameroon, cocoa trees are mostly grown in forests and without fertilization. Our aim was to learn more about the temporal dynamics of soils in cocoa agroforests by comparing young (1-4 years old) and old (over 25 years old) cocoa agroforests. Short fallow and secondary forest were used as treeless and forest references. The numbers and diversities of soil vesicular arbuscular mycorrhizal (VAM) fungi on 60 cocoa producing farms in the Central province of Cameroon were assessed based on the classical morphotyping of spore morphology. We also observed the soil organic matter, nitrogen and major soil nutrients. VAM spore density was significantly lower in the young cocoa agroforests (16 spores g-1 dry soil) than in the old cocoa agroforests (36 spores g-1 dry soil). Levels in the nearby secondary forest (46 spores g-1 dry soil) were not significantly different from old cocoa. The spore density was significantly highest in the short fallow (98 spores g-1 dry soil). The Shannon- Weaver index also showed significantly lower biodiversity in young cocoa (0.39) than in old cocoa agroforests (0.48), secondary forest (0.49) and short fallow (0.47). These observations were supported by significant differences in the C:N ratio, Ca, Mg, and cation exchange capacity between young and old cocoa agroforests. We concluded that unfertilized cocoa agroforests could be sustainable, despite a decrease in some soil characteristics at a young stage, due to traditional land-conversion practices based on selective clearing and burning of secondary forest. (Résumé d'auteur

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“…Lower AMF species richness has been found in arable fields, while species-rich AMF communities were detected in different natural ecosystems and perennial communities such as tropical forest (Snoeck et al, 2010). Studies from the tropics indicate that the AMF species richness in a monoculture like sugarcane grown in fertile soils (Colombian Mollisols) can be high (Sieverding, 1991).…”

Assessing the temporal stability of spatial patterns of soil apparent electrical conductivity using geophysical methods

“…Once established, cacao remains in the same field for decades, therefore cocoa fields are dominated with aging trees growing on variable and depleted soils (Snoeck et al, 2010). In Trinidad and Tobago like many cocoa producing countries, increase in cocoa production is mainly due to expansion of existing farms or creation of new farms rather than increase in yield per unit area (Gockowski, 2007;Snoeck et al, 2010).…”

“…Once established, cacao remains in the same field for decades, therefore cocoa fields are dominated with aging trees growing on variable and depleted soils (Snoeck et al, 2010). In Trinidad and Tobago like many cocoa producing countries, increase in cocoa production is mainly due to expansion of existing farms or creation of new farms rather than increase in yield per unit area (Gockowski, 2007;Snoeck et al, 2010). While technological approaches to address within-field variability have resulted in stupendous increase in yield per unit area in the production of other crops, cocoa production still relies on inefficient and outdated traditional production and management methods that do not take into account withinfield soil variability.…”